1. Field of the Invention
The present invention is directed toward a method of receiving torque reduction or torque limitation requests in a vehicle control system.
2. Description of Related Art
Synergistic operation of multiple vehicle control systems is preferred and a method to provide such operation is provided through a cooperative control system. In a typical cooperative control system design, a top level electronic control unit (ECU) having a top level algorithm evaluates and controls the overall strategy for vehicle dynamics such as traction control, stability control, body motion control, etc. The top level ECU then controls ECUs within individual vehicle control systems to meet the goals of the overall strategy.
The cooperative control system may include a vehicle stability assist (hereinafter VSA) individual control system. The VSA system is controlled by an ECU subordinate to the top level ECU. The VSA system works by controlling brake pressure, engine torque, and/or individual wheel torque to help maintain traction between the vehicle wheels and a road surface. Specifically, detrimental effects caused by oversteer and understeer can be combated through adjustment of the torques and brake pressure. The VSA system ECU, in turn, sends commands and requests to other systems, for example, the vehicle's four-wheel-drive (4WD) system. An ECU dedicated to the 4WD system receives and implements the commands and requests sent by the VSA ECU.
However, because the 4WD system is strongly manipulated by feed-forward control whereas the VSA system is not, requests sent from the VSA system to the 4WD system are often contradictory to requests provided directly by the 4WD system. As a result, in combination, the VSA and 4WD systems may not perform efficiently. Additionally, erroneous requests supplied by the VSA system can be implemented by the 4WD system without being checked.